1. Field of the Invention
The present invention relates to a liquid jet head for ejecting a liquid from a nozzle to form images, characters, or a thin film material onto a recording medium. The present invention relates also to a liquid jet apparatus using the liquid jet head, and to a manufacturing method for the liquid jet head.
2. Description of the Related Art
In recent years, there has been used an ink-jet type liquid jet head for ejecting ink drops on recording paper or the like to draw and record characters or figures thereon, or for ejecting a liquid material on a surface of an element substrate to form a functional thin film thereon. Further, there has been used a liquid jet apparatus using the above-mentioned ink-jet type liquid jet head. In the ink-jet type liquid jet head, the ink or the liquid material is supplied from a liquid tank through a supply pipe into the liquid jet head, and then the ink is ejected from the nozzle of the liquid jet head to record the characters or the figures, or the liquid material is ejected to form the functional thin film having a predetermined shape.
FIG. 9 is a schematic sectional view of an ink-jet head 100 of the above-mentioned type described in Japanese Patent Translation Publication No. 2000-512233. The ink-jet head 100 has a three-layer structure of a cover 125, a PZT sheet 103 formed of a piezoelectric body, and a bottom cover 137. The cover 125 includes nozzles 127 for discharging small drops of ink. In an upper surface of the PZT sheet 103, there are formed ink channels 107 formed of an elongated groove having a cross-section having a convex shape toward a bottom thereof. The plurality of ink channels 107 are formed so as to be parallel to each other in a direction orthogonal to a longitudinal direction. Further, the ink channels 107 adjacent to each other are defined by side walls 113. An upper side-wall surface of each of the side walls 113, there is formed an electrode 115. Also in a side wall surface of the ink channels 107 adjacent to each other, there is formed an electrode. Therefore, each of the side walls 113 is sandwiched between the electrode 115 and the electrode (not shown) formed on each of the side wall surfaces of each of the ink channels adjacent to each other.
The ink channels 107 are communicated to the nozzles 127, respectively. In the PZT sheet 103, there are formed, from a back side, a supply duct 132 and a discharge duct 133. The supply duct 132 and the discharge duct 133 are communicated to the ink channel 107 and to vicinities of both end portions of the ink channel 107. The ink is supplied through the supply duct 132, and the ink is discharged through the discharge duct 133. On a top surface of the PZT sheet 103, and at a right end portion and a left end portion of the ink channel 107, there are formed concave portions 129, respectively. In a bottom surface of each of the concave portions 129, there is formed an electrode, which is electrically conducted to the electrode 115 formed on the side wall surface of each of the ink channels 107. A connection terminal 134 is received in the concave portion 129. The connection terminal 134 is electrically connected to an electrode (not shown) formed on a bottom surface of the concave portion 129.
FIG. 10 illustrates a schematic sectional view of the portion AA of FIG. 9. The respective side walls 113a to 113e define the ink channels 107a to 107e, respectively. Driving electrodes a1, a2 . . . e1, e2 are disposed so as to sandwich both side surfaces of the respective side walls 113a to 113e, respectively. The respective electrodes a1, a2 . . . e1, e2 are connected to the connection terminal 134 illustrated in FIG. 9 on the right side or the left side. The respective ink channels 107a to 107e are communicated to the discharge duct 133. The ink is supplied through the supply duct 132 (not shown), and is discharged through the discharge duct 133.
The ink-jet head 100 is operated as follows. The ink supplied from the supply duct 132 fills the ink channels 107, and is discharged through the discharge duct 133. In other words, the ink flows so as to circulate the supply duct 132, the ink channels 107, and the discharge duct 133. For example, for driving the ink channels 107a, the electrodes a2 and b1 are set to the common low electric potential, and a high driving-voltage is applied to the electrodes a1 and b2.
Then, the side walls 113a and 113b are deformed due to a piezoelectric thickness slip effect, and hence volume of the ink channels 107a is changed. In this way, the ink is ejected through the nozzles 127. In this case, the electrode b2 of the ink channel 107b adjacent to the ink channel 107a is used to eject the ink from the ink channel 107a. Therefore, the ink channel 107b adjacent to the ink channel 107a cannot be driven simultaneously and independently with respect to the ink channels 107a. In this case, the ink channels 107a, 107c, 107e are independently driven alternately as such. For example, regarding the ink channel 107c, the electrodes c2 and d1 are set to the common electric potential, and the driving voltage is applied to the electrodes c1 and d2, to thereby eject the ink.
In the above-mentioned ink-jet discharging method, the ink circulates always through the supply duct 132 and the discharge duct 133. Therefore, even if foreign matters such as bubbles and dust are entered and mixed into the ink channels 107, it is possible to rapidly discharge the foreign matters to an outside. Thus, it is possible to prevent such a failure that the ink can not be ejected due to clogging of the nozzles or a printing density is fluctuated.
However, in the above-mentioned conventional example of FIG. 9, a high-degree of technology is required to form the supply duct 132 and the discharge duct 133 in vicinities of the both ends in the longitudinal direction of each of the ink channels 107. Each of the plurality of ink channels 107 formed so as to be parallel to each other in the top surface of the PZT sheet 103 has, for example, a groove width of from 70 to 80 μm, a groove depth of from 300 to 400 μm, and a groove length of from several millimeters to 10 mm, and each of the walls defining the ink channels 107 adjacent to each other has a thickness of from 70 to 80 μm. The groove of the ink channel 107 is formed by grinding under a state in which a dicing blade, which is obtained through embedding abrasive grains such as diamonds in an outer peripheral portion of a thin disk, is rotated at high speed. Therefore, a cross-section of the groove has a convex shape in the depth direction. In particular, profile of a grinding blade is transferred to the vicinities of the both ends in the longitudinal direction of the groove.
As a forming method for the ink channels 107 illustrated in FIG. 9, a case of forming the supply duct 132 and the discharge duct 133 after the plurality of grooves are formed is first taken into consideration. The supply duct 132 and the discharge duct 133 are required to be communicated to each other in the bottom portions of the plurality of grooves. However, in the vicinities of the both ends in the longitudinal direction of the each of the grooves, the bottom surface of the each of the grooves is not flat. Therefore, it is extremely difficult to form the supply duct 132 and the discharge duct 133 so as to conform to the bottom surface of each of the grooves. Further, when the PZT sheet 103 is subjected to the cutting from the back side, the deepest portion of the groove is first opened, and then the opening portion is gradually extended. However, when a part of the bottom surface of the groove is opened, the side walls in vicinity of the opening portion are not supported anymore. Therefore, it is extremely difficult to grind the supply duct 132 and the discharge duct 133 without breaking the thin side walls 113 of the groove including the opened bottom portion. Further, the electrodes are formed on the side walls defining the grooves. When the PZT sheet 103 is deeply cut from the back side, there are problems in that the electrode formed on the side wall of the groove is also unfortunately cut, in that the voltage for driving the side wall is varied because resistance of the electrode is increased, and the like.
In addition, when the supply duct 132 and the discharge duct 133 are tried to be formed in a region in which the bottom surface of the groove is flat, the ink does not circulate anymore at the both end portions in the longitudinal direction of the groove. Therefore, stagnation of the ink occurs, the bubbles and the dust are remained in the stagnation. As a result, advantage in the above-mentioned process of preventing clogging in the nozzles 127 and the like by removing the foreign matters from the ink channels 107 while the ink circulates is deteriorated.
Meanwhile, the following method is conceivable. Specifically, in the method, the supply duct 132 and the discharge duct 133 are first formed from a back side of the PZT sheet 103, and then the grooves are formed from a front side of the PZT sheet 103. In this case, the supply duct 132 and the discharge duct 133 are easy to be cut, but high precision of control is required for forming the grooves. The dicing blade has a diameter generally ranging from 2 inches to 4 inches. For example, in a case of forming a groove having, for example, a depth of 350 μm in the PZT sheet 103 from the front side thereof with use of the dicing blade having the diameter of 2 inches, if an allowance for the depth of the groove is supposed to 10 μm, an allowance for the length of the groove is about 120 μm which is 12 times as large as the depth of the groove. In a case of using the dicing blade having the diameter of 4 inches, the allowance in the longitudinal direction is about 16 times as large as the allowance in the depth direction. Therefore, it is extremely difficult to cause the opening end portions of the supply duct 132 and the discharge duct 133 to correspond to the end portions in the longitudinal direction of the groove, respectively. If positional shifting occurs between the end portion in the longitudinal direction of the groove and an outer peripheral end portion of the supply duct 132, or between the end portion in the longitudinal direction of the groove and an outer peripheral end portion of the discharge duct 133, the stagnation or resistance of an ink flow still occurs in the end portions of the ink channel 107. As a result, in the above-mentioned process, the advantage of preventing the clogging in the nozzles 127 through causing the ink to circulate is deteriorated.
Further, in the ink-jet head 100 described in Japanese Patent Translation Publication No. 2000-512233, the connection terminal 134 is received in the concave portion 129 formed on the top surface of the PZT sheet 103, and an outer surface of the cover 125 is formed into a flat surface. The electrode formed on a lower surface of the connection terminal 134 and the electrode formed on the side wall surface of the side wall defining the ink channels 107 are electrically connected to each other through intermediation of the side wall surface, the top surface of the PZT sheet 103, and the bottom surface of the concave portion 129. A large number of ink channels 107 are collectively formed in the direction orthogonal to the longitudinal direction, and hence it is necessary that the electrodes of the respective side walls be electrically separated from each other. Therefore, also in the top surface of the PZT sheet 103 and the bottom surface of the concave portion 129, it is necessary that the large number of the electrodes be similarly formed so as to be electrically separated from each other at high density. However, in particular, the bottom surface of the concave portion 129 is curved, a high-definition of patterning technology is required for highly-accurately forming an electrode pattern in the curved surface.
Further, although described that the ink channels 107a, 107c, 107e are simultaneously, independently driven, and alternately as such, it is impossible that the ink channels 107a, 107c, 107e are sequentially and simultaneously driven in a case where the ink is electrically conductive. That is, when the electrically conductive ink is used, in the structures in FIG. 9 and FIG. 10, the electrode on a high voltage side and the electrode on a low voltage side are put into an electrically short-circuit state. Therefore, it is impossible to achieve an electrical potential gradient required for the side wall including the piezoelectric body, and hence it is primarily impossible to drive the piezoelectric body. In addition, there is the possibility that the electrodes become electrolyzed, and that the driving electrical system is broken.